DE102024000328B3 - Electric drive system and charging method - Google Patents

Abstract

The invention relates to an electric drive system for a vehicle, comprising an electric machine (2) with three stator windings (L1, L2, L3), a high-voltage battery (3) and an inverter (1) for supplying voltage to the electric machine (2), wherein the inverter (1) has three half-bridges (HB1, HB2, HB3), each formed from two semiconductor switches (S1 to S6), to whose center taps one of the stator windings (L1, L2, L3) is connected, wherein a DC connection box (4) for charging the high-voltage battery (3) by means of a direct voltage and/or an AC connection box (5) for at least single-phase charging of the high-voltage battery (3) by means of an alternating voltage is arranged, wherein
- a diode (D1) or a semiconductor with diode function is arranged between the center tap of one of the half-bridges (HB1 to HB3) and a contact of the AC connection box (5) and/or the DC connection box (4) with reverse polarity,
- a diode (D2) or a semiconductor with diode function is arranged between the center tap of another of the half-bridges (HB1 to HB3) and another contact of the AC junction box (5) and/or the DC junction box (4) with reverse polarity,
- one diode (D3, D4) or one semiconductor with diode function is arranged from a negative high-voltage potential (HV-) of the inverter (1) to each of the two contacts of the AC connection box (5) and/or the DC connection box (4) with forward polarity.

Description

The invention relates to an electric drive system for a vehicle according to the preamble of claim 1 and to a method for charging a high-voltage battery of the electric drive system according to the preamble of claim 7 or 8.

• - einer Schaltvorrichtung, welche aufweist:
• - einen ersten Schaltzustand, in welchem ein Ladeanschluss mit einem elektrischen Energiespeicher des Fahrzeugs direkt verbunden ist, sodass der elektrische Energiespeicher mit einer Eingangsspannung, welche am Ladeanschluss anliegt, aufladbar ist,
• - einen zweiten und dritten Schaltzustand, in welchem der Ladeanschluss über einen Wechselrichter mit dem elektrischen Energiespeicher verbunden ist, sodass der elektrische Energiespeicher in Abhängigkeit von dem Wechselrichter aufladbar ist.

DE 10 2021 003 883 A1 describes an electric drive system for a vehicle with

• - a switching device which comprises:
• - a first switching state in which a charging connection is directly connected to an electrical energy storage device of the vehicle, so that the electrical energy storage device can be charged with an input voltage applied to the charging connection,
• - a second and third switching state in which the charging connection is connected to the electrical energy storage device via an inverter, so that the electrical energy storage device can be charged depending on the inverter.

• - einer elektrischen Drehstrommaschine zum Antreiben des Fahrzeugs,
• - einem elektrischen Energiespeicher zum elektrischen Versorgen der elektrischen Drehstrommaschine während eines Fahrbetriebs des Fahrzeugs,
• - einem Wechselrichter der elektrischen Drehstrommaschine, welcher mit dem elektrischen Energiespeicher elektrisch gekoppelt ist, und
• - einem fahrzeugseitigen Ladeanschluss zum elektrischen Koppeln des elektrischen Energiespeichers mit einer fahrzeugexternen Ladeeinheit, wobei
• - in Abhängigkeit von dem Wechselrichter eine Ladespannung des fahrzeugseitigen Ladeanschlusses in eine Versorgungsspannung zum Laden des elektrischen Energiespeichers umwandelbar ist.

DE 10 2021 003 852 A1 describes an electric drive system for a vehicle with

• - an electric three-phase machine to drive the vehicle,
• - an electrical energy storage device for supplying the three-phase electric machine with electricity while the vehicle is in operation,
• - an inverter of the three-phase electric machine, which is electrically coupled to the electrical energy storage device, and
• - a vehicle-side charging connection for electrically coupling the electrical energy storage device with a vehicle-external charging unit, wherein
• - depending on the inverter, a charging voltage of the vehicle-side charging connection can be converted into a supply voltage for charging the electrical energy storage device.

From the CN 215793 231 U An integrated structure comprising an inverter, a charger, and a motor winding is known, with the inverter being connected between an HV battery and a motor with the motor winding for its operation. An AC power supply is connected via a rectifier bridge through one terminal to an output phase of the inverter and through another terminal to an HV DC phase of the inverter and thus to the HV battery.

The invention is based on the object of providing a novel electric drive system for a vehicle and a novel method for charging a high-voltage battery of the electric drive system.

The object is achieved according to the invention by an electric drive system for a vehicle having the features of claim 1 and a method for charging a high-voltage battery of the electric drive system having the features of claim 7 or 8.

Advantageous embodiments of the invention are the subject of the subclaims.

• - eine Diode oder ein Halbleiter mit Diodenfunktion zwischen dem Mittelabgriff einer der Halbbrücken und einem Kontakt der AC-Anschlussdose und/oder der DC-Anschlussdose in Sperrrichtung gepolt angeordnet,
• - eine Diode oder ein Halbleiter mit Diodenfunktion zwischen dem Mittelabgriff einer anderen der Halbbrücken und einem anderen Kontakt der AC-Anschlussdose und/oder der DC-Anschlussdose in Sperrrichtung gepolt angeordnet,
• - je eine Diode oder je ein Halbleiter mit Diodenfunktion von einem negativen Hochvoltpotential des Inverters zu jedem der beiden Kontakte der AC-Anschlussdose und/oder der DC-Anschlussdose in Durchlassrichtung gepolt angeordnet.

An electric drive system for a vehicle is proposed, comprising an electric machine with three stator windings for driving the vehicle, a high-voltage battery, and an inverter for converting a direct voltage of the high-voltage battery into an alternating voltage for supplying the electric machine. The inverter comprises a B6 bridge consisting of three half-bridges, each formed from two semiconductor switches, to whose center taps one of the stator windings is connected. Furthermore, a DC connection box for charging the high-voltage battery using a direct voltage and/or an AC connection box for at least single-phase charging of the high-voltage battery using an alternating voltage is provided. According to the invention,

• - a diode or a semiconductor with diode function is arranged between the center tap of one of the half-bridges and a contact of the AC junction box and/or the DC junction box, polarized in the reverse direction,
• - a diode or a semiconductor with diode function is arranged between the center tap of another of the half-bridges and another contact of the AC junction box and/or the DC junction box, polarized in the reverse direction,
• - one diode or one semiconductor with diode function arranged from a negative high-voltage potential of the inverter to each of the two contacts of the AC connection box and/or the DC connection box, polarized in the forward direction.

In one embodiment, the semiconductor switches and/or the semiconductors with diode function are designed as MOSFETs or IGBTs with freewheeling diodes.

In one embodiment, the inverter has an intermediate circuit capacitor.

In one embodiment, the inverter has current measuring devices for measuring the alternating current between the center taps of the half-bridges and the stator windings.

In one embodiment, two relay contacts are arranged between the respective conductor and the connected diodes to de-energize two conductors, including a phase conductor and a neutral conductor, of the AC junction box. Alternatively or additionally, two relay contacts are arranged between the respective conductor and the connected diodes to de-energize two conductors, including a positive potential conductor and a negative potential conductor, of the DC junction box.

In one embodiment, one relay contact assigned to the DC connection box and one relay contact assigned to the AC connection box are connected to each other to form a pair in the direction of the inverter.

According to one aspect of the present invention, a method for charging the high-voltage battery of the described electric drive system at a DC charging station with a boost function is proposed, wherein the DC charging station is connected to the DC junction box. According to the invention, a semiconductor switch arranged as a low-side switch of one of the half-bridges, which is connected to the DC junction box via one of the diodes, is controlled in a clocked manner.

According to a further aspect of the present invention, a method for charging the high-voltage battery of the described electric drive system at an AC charging station is proposed, wherein the AC charging station is connected to the AC junction box. According to the invention, during a positive half-wave of an alternating voltage fed in by the AC charging station, a semiconductor switch arranged as a low-side switch of one of the half-bridges, which is connected to the DC junction box via one of the diodes, is controlled in a clocking manner, wherein during a negative half-wave of the alternating voltage fed in by the AC charging station, a semiconductor switch arranged as a low-side switch of another of the half-bridges, which is connected to the DC junction box via one of the diodes, is controlled in a clocking manner.

In one embodiment, when the low-side switch is open, the semiconductor switch of the same half-bridge arranged as a high-side switch can be closed as soon as a current flows through its body diode or freewheeling diode.

In one embodiment, a target current is regulated by timing the semiconductor switches.

The inventive solution eliminates the need for contactors to isolate the star point of the electric machine. The boost function utilizes the main inductances of the electric machine's stator windings. The electric machine and inverter can be used as a single-phase PFC. Furthermore, the electric machine and inverter can be used as a boost DC/DC converter, for example, from 400 V to 800 V. The inventive solution prevents battery short circuits in the event of an insulation fault in the vehicle and varistor triggering in the charging station (Chademo problem).

Embodiments of the invention are explained in more detail below with reference to drawings.

• 1 eine schematische Ansicht eines Inverters zum Betrieb einer elektrischen Maschine mit einer Beschaltung, einschließlich einer DC-Anschlussdose und einer AC-Anschlussdose,
• 2 eine schematische Ansicht einer vereinfachten Beschaltung des Inverters,
• 3 eine schematische Ansicht einer weiter vereinfachten Beschaltung des Inverters,
• 4 eine schematische Ansicht der vereinfachten Beschaltung des Inverters gemäß 2 beim Laden an einer DC-Ladestation mit Boost-Funktion,
• 5 ein schematisches Diagramm mit Signalen einer Simulation des Inverters beim Laden an einer DC-Ladestation mit Boost-Funktion,
• 6 ein schematisches Diagramm mit Signalen der Simulation des Inverters beim Eintreten von Isolationsfehlern,
• 7 ein schematisches Diagramm mit weiteren Signalen der Simulation des Inverters zur Veranschaulichung einer Potentialverteilung,
• 8 eine schematische Ansicht der Beschaltung des Inverters beim Laden an einer AC-Ladestation während einer positiven Halbwelle,
• 9 eine schematische Ansicht der Beschaltung des Inverters beim Laden an der AC-Ladestation während einer negativen Halbwelle,
• 10 ein schematisches Diagramm mit Signalen einer Simulation des Inverters beim Laden an der AC-Ladestation,
• 11 ein schematisches Diagramm mit Signalen der Simulation des Inverters beim AC-Laden zu Beginn der positiven Halbwelle, und
• 12 ein schematisches Diagramm mit Signalen der Simulation des Inverters beim AC-Laden zu Beginn der negativen Halbwelle.

Showing:

• 1 a schematic view of an inverter for operating an electrical machine with a circuit, including a DC connection box and an AC connection box,
• 2 a schematic view of a simplified circuit of the inverter,
• 3 a schematic view of a further simplified circuit of the inverter,
• 4 a schematic view of the simplified circuit of the inverter according to 2 when charging at a DC charging station with boost function,
• 5 a schematic diagram with signals from a simulation of the inverter when charging at a DC charging station with boost function,
• 6 a schematic diagram with signals of the simulation of the inverter when insulation faults occur,
• 7 a schematic diagram with further signals of the inverter simulation to illustrate a potential distribution,
• 8 a schematic view of the inverter circuitry when charging at an AC charging station during a positive half-wave,
• 9 a schematic view of the inverter circuitry when charging at the AC charging station during a negative half-wave,
• 10 a schematic diagram with signals from a simulation of the inverter during charging at the AC charging station,
• 11 a schematic diagram with signals of the simulation of the inverter during AC charging at the beginning of the positive half-cycle, and
• 12 a schematic diagram with signals from the simulation of the inverter during AC charging at the beginning of the negative half-cycle.

Corresponding parts are provided with the same reference numerals in all figures.

1 is a schematic view of an inverter 1 for operating an electrical machine 2, for example a drive motor of an electrically powered vehicle, in particular a passenger car, a commercial vehicle, or a bus. The inverter 1 has a B6 bridge consisting of three half-bridges HB1, HB2, HB3, each formed from two semiconductor switches S1 to S6, in particular MOSFETs or IGBTs with a freewheeling diode. Furthermore, the inverter 1 has an intermediate circuit capacitor C and current measuring devices A, in particular for measuring alternating current, at the center taps of the half-bridges HB1 to HB3. The electrical machine 2 has three stator windings L1 to L3, which are connected to the center taps of the half-bridges HB1 to HB3.

The inverter 1 is configured by means of appropriate wiring to be used when charging a high-voltage battery 3 of the vehicle by means of direct voltage via a DC connection box 4 and by means of a single-phase alternating voltage via an AC connection box 5.

The circuit comprises two relays or relay contacts L, N for de-energizing two conductors, in particular a phase conductor and a neutral conductor, of the AC junction box 5. Furthermore, two relays or relay contacts EVSE_P, EVSE_N are arranged for de-energizing two conductors, in particular a positive potential conductor and a negative potential conductor, of the DC junction box. In the direction of the inverter 1, one relay contact L, N and one relay contact EVSE_P, EVSE_N are connected to each other to form a pair, for example, relay contact L is connected to relay contact EVSE_P, and relay contact N is connected to relay contact EVSE_N.

Furthermore, a diode D1 is arranged between the center tap of one of the half-bridges HB1 to HB3, for example the half-bridge HB1, and a pair of the interconnected relay contacts L, EVSE_P polarized in the reverse direction.

Furthermore, a diode D2 is arranged between the center tap of another of the half-bridges HB1 to HB3, for example the half-bridge HB2, and the other pair of interconnected relay contacts N, EVSE_N, polarized in the reverse direction.

Furthermore, one diode D3, D4 is arranged in the forward direction from a negative high-voltage potential HV- of the inverter 1 to each pair of the interconnected relay contacts L, EVSE_P and N, EVSE_N.

Instead of the diodes D1 to D4, an alternative semiconductor component with diode function can also be used, for example a MOSFET with a body diode in the direction of the respective diode, an IGBT with a corresponding freewheeling diode, etc.

For charging a high-voltage battery 3 of a battery-electric vehicle at a DC charging station 6, which provides a maximum output voltage (for example 500 V) that is lower than a nominal voltage (for example 800 V) of the high-voltage battery 3, various solutions are known in the prior art, for example a switching battery, a separate boost DC/DC converter, etc.

The present invention proposes a solution in which, during DC charging, a DC charging station 6 is connected to the inverter 1 and the electric machine 2 via the DC junction box 4, the relay contacts EVSE_P, EVSE_N, and at least one or more of the diodes D1, D2, D3, D4 in such a way that the function of a galvanically coupled DC/DC converter can be realized only by means of a special control of at least one or more of the semiconductor switches S1 to S6. Since the current flow through the stator windings L1 to L3 represents a realistic operating point of the electric machine 2, the entire stator inductance can be used. The electric machine 2 nevertheless does not move.

In the event of an insulation fault in the vehicle, this can directly result in insulation overload at the opposite HV_N potential of the DC charging station 6. Protective varistors in the DC charging station 6 cause a short circuit in the high-voltage battery 3. The problem of a battery short circuit (several thousand amperes) is avoided in the proposed architecture by diode D4. Furthermore, it is important that the respective semiconductor switches S1 to S6 in inverter 1 are no longer activated (switched on) in the event of this double insulation fault. However, a short circuit in the DC charging station 6 may remain.

2 is a schematic view of a simplified circuit of the inverter 1 without the AC connection box 5 (shown in 1 ) and the Relay contacts L, N (shown in 1 ). The diode D4 serves to prevent the short circuit of the high-voltage battery 3 as a result of an insulation fault of the positive high-voltage potential HV+ to a potential equalization PA in the vehicle and, as a result, an insulation fault of a negative high-voltage potential HV_N (shown in 7 ) for potential equalization PA in the DC charging station 6. With the arrangement shown, the boost function can be implemented when charging at a DC charging station 6.

3 is a schematic view of a simplified circuit of the inverter 1 without the AC connection box 5 (shown in 1 ), the relay contacts L, N (shown in 1 ) and the diodes D1 to D3 (shown in 1 Instead of via diode D1, the relay contact EVSE_P is connected directly to the center tap of half-bridge HB1. The arrangement shown is the minimum configuration for implementing the boost function when charging at a DC charging station 6.

4 is a schematic view of the simplified circuit of the inverter 1 according to 2 when charging at the DC charging station 6 with boost function. The semiconductor switch S4, i.e. the low-side switch of one of the half-bridges HB1 to HB3, in particular the half-bridge HB2, is controlled in a clocked manner. When the semiconductor switch S4 is closed, a current 11 flows from the DC charging station 6 via the relay contact EVSE_P, the diode D1, the stator winding L1, the star point of the electric machine 2 (shown in 1 ), the stator winding L2, the semiconductor switch S4, the diode D4 (shown in 1 ) and the relay contact EVSE_N back to the DC charging station 6. When the semiconductor switch S4 is open, a current I2 flows from the DC charging station 6 via the relay contact EVSE_P, the diode D1, the stator winding L1, the star point of the electric machine 2, the stator winding L2, the body diode of the semiconductor switch S3, the high-voltage battery 3, the diode D4 and the relay contact EVSE_N back to the DC charging station 6.

Out of 4 It can be seen that only two of the four diodes D1 to D4, namely diodes D1 and D4, are required for the boost function. They can also be replaced by MOSFETs for optimization at higher currents. Unlike the state of the art, they offer the advantage of avoiding a battery short circuit in the event of an insulation fault (Chademo problem).

As soon as the controlled semiconductor switch S4 is closed, the two stator windings L1 and L2 are supplied with the voltage of the DC charging station 6. The current I1 through the two stator windings L1 and L2 increases. During this phase, the high-voltage battery 3 is not charged. If the controlled semiconductor switch S4 is opened, the only possible freewheeling path for the current I2 impressed in the stator windings L1 and L2 is via the body diode of the high-side switch located in the same half-bridge, in this case the semiconductor switch S3. To optimize losses, this semiconductor switch S3 can be closed as soon as the current I2 flows. The resulting current path leads via the high-voltage battery 3, so that it is charged.

5 is a schematic diagram with signals from a simulation of inverter 1 (shown in 1 ) with the circuitry, whereby the boost function is connected to a DC charging station 6 (shown in 1 ) with 400 V. A nominal current was specified within the limits of 120 A to 125 A. In the following two diagrams, the currents of the stator windings L1, L2, L3 (shown in 1 ) and a control signal Gate_S4 for controlling the semiconductor switch S4 (shown in 1 ). At a time t=0.5 s, an insulation fault occurs in the vehicle from the positive high-voltage potential HV+ to the potential equalization PA. At a time t=0.6 s, the clock operation of the semiconductor switch S4 is stopped and the semiconductor switch S4 remains open. At a time t=0.7 s, a second insulation fault occurs in the DC charging station 6 from the negative high-voltage potential HV_N- (shown in 1 ) for potential equalization PA.

• Isolationswiderstände: 1 MOhm
• Induktivität der Statorwicklungen L1, L2, L3: 1000 µF
• Innenwiderstand Ri_Batt (dargestellt in 1) der Hochvolt-Batterie 3 (dargestellt in 1) und der DC-Ladestation 6: 0,1 Ohm

The following parameters were used for the simulation:

• Insulation resistance: 1 MOhm
• Inductance of the stator windings L1, L2, L3: 1000 µF
• Internal resistance Ri_Batt (shown in 1 ) of the high-voltage battery 3 (shown in 1 ) and the DC charging station 6: 0.1 Ohm

In 5 are a source voltage U_Q of the DC charging station 6, the control signal Gate_S4 for controlling the semiconductor switch S4, a current I_HV+ in the positive high-voltage potential HV+ (shown in 1 ), a current I_HV- (shown in 1 ) in the negative high-voltage potential HV-, a current I_Q from the DC charging station 6 and a charging current I_L flowing into the high-voltage battery 6.

When the semiconductor switch S4 is closed, the current in the two stator windings L1, L2 increases. It can be seen that the current I_Q of the DC charging station 6 is identical to the current in the stator windings L1, L2. During this time, the high-voltage battery 3 is not charged (current I_L = 0). The current increases during this phase until it reaches the setpoint of 125 A. Normally, however, this would be limited by the large intermediate circuit capacitor C (shown in 1 ) of the Inver 1 is still present. However, it has been omitted here to better illustrate the function. As soon as the semiconductor switch S4 opens upon reaching 125 A, the current I_Q of the DC charging station 6 flows through both the stator windings L1, L2, as well as through the high-voltage battery 3. The current I_Q decreases. Once the value falls below 120 A, the semiconductor switch S4 closes again.

6 is a schematic diagram with signals of the simulation of inverter 1 (shown in 1 ) with the circuit when insulation faults occur: Over the entire time window of the simulation, an insulation fault occurs in the vehicle from the positive high-voltage potential HV+ (shown in 1 ) for potential equalization PA (insulation value is ideal short circuit, i.e. 0 Ohm, time t= 0.5s). In this state, the circuit still functions correctly, i.e. inverter 1, which works as a booster, can set the target current and thus charges the high-voltage battery 3 (shown in 1 ). There are no short-circuit currents in the high-voltage battery 3 or the DC charging station 6 (shown in 1 ). From the time t = 0.6s, the timing of the semiconductor switch S4 (shown in 1 ) is set. As soon as the timing of the semiconductor switch S4 is set, the charging current I_L from the DC charging station 6 to the high-voltage battery 3 ends. There are still no short circuits.

From the time t = 0.7s, the second insulation fault from the negative high-voltage potential HV_N (shown in 7 ) to the equipotential bonding PA in DC charging station 6. No short-circuit current is generated in DC charging station 6, but a current is generated, which is very high here due to the relatively low assumed value of 0.1 mOhm. In reality, this would mean that DC charging station 6 is set to the maximum current commanded by the vehicle, or the current corresponds to the maximum current of its power electronics (for example, a possible value when commanded by the vehicle is 150 A, or 500 A at the maximum current of DC charging station 6).

7 is a schematic diagram with further signals of the simulation of inverter 1 (shown in 1 ) with the circuitry to illustrate the potential distribution.

In the simulation, the high-voltage potentials HV_P, HV_N of the DC charging station 6 (shown in 1 ) in the vehicle. This is particularly interesting when considering insulation faults. Before t = 0.5 s, the insulation is still intact. A uniform distribution of the insulation resistances is assumed (1 MOhm each). This results in an almost symmetrical high-voltage distribution in the vehicle (500 V HV+ to PA and 300 V HV- to PA). The high-voltage distribution from HV- to PA of the vehicle is transferred to the DC charging station 6 side, since the booster function is a galvanically coupled booster with a common negative high-voltage potential HV-, HV_N. The negative high-voltage potential HV_P is reduced at DC charging station 6 by the value of the booster, i.e., starting from a voltage from HV+ to PA of 500 V in the vehicle and a voltage increase by the booster of 400 V, the voltage between HV_P and PA on the DC charging station 6 side is 100 V.

From the occurrence of the first insulation fault in the vehicle at t=0.5 s, the potentials in both the vehicle and the DC charging station 6 shift downwards by 500 V. As soon as the clocking of the semiconductor switch S4 (shown in 1 ) is stopped, the voltage difference between the high-voltage battery 3 (shown in 1 ) (800 V) and the DC charging station 6 (400 V) at the diode D4 (shown in 1 ). Since HV_P is identical to PA, HV_N is now below PA (-400V) by the amount of the voltage of DC charging station 6.

Starting at t=0.7s, a second insulation fault is assumed in DC charging station 6 from HV_N to PA. This insulation fault is also assumed to be an ideal short circuit with 0 ohms. This results in a potential distribution of 0 V from HV_P to PA and, at the same time, 0 ohms from HV_N to PA on the DC charging station 6 side. However, this should only be considered a theoretical distribution, since it can be assumed that an insulation fault, although low-resistance, will never reach 0 ohms.

8 is a schematic view of the circuitry of inverter 1 when charging at an AC charging station 7. To enable single-phase AC charging, a pair of diodes D1, D3 is connected to relay contact L for the phase conductor, and the second pair of diodes D2, D4 is connected to relay contact N for the neutral conductor. In the embodiment shown, the pair of diodes D1, D3 assigned to the first half-bridge HB1 was selected for relay contact L for the phase conductor, and the pair of diodes D2, D4 assigned to the second half-bridge HB2 was selected for relay contact N for the neutral conductor. In other embodiments, other variants for connecting relay contacts N and L to the diode pairs can also be selected.

During the positive half-wave of the alternating voltage supplied by the AC charging station 7, the circuit functions identically to the booster function shown above. The timing of semiconductor switch S4 regulates the current to a target value. This target current depends on the current instantaneous value of the alternating voltage. Such control methods correspond to the state of the art for regulating alternating currents using power factor correction (PFC). When the semiconductor switch S4 is closed, a current 11 flows from the AC charging station 7 via the relay contact L, the diode D1, the stator winding L1, the star point of the electrical machine 2 (shown in 1 ), the stator winding L2, the semiconductor switch S4, the diode D4 and the relay contact N back to the AC charging station 7. When the semiconductor switch S4 is open, a current I2 flows from the AC charging station 7 via the relay contact L, the diode D1, the stator winding L1, the star point of the electric machine 2, the stator winding L2, the body diode of the semiconductor switch S3, the high-voltage battery 3, the diode D4 and the relay contact N back to the AC charging station 7.

9 is a schematic view of the circuitry of inverter 1 when charging at an AC charging station 7 during the negative half-wave of the AC voltage fed in by the AC charging station 7. In the negative half-wave of the AC voltage, the current flow is reversed compared to the positive half-wave. Accordingly, a low-side switch, for example, semiconductor switch S2 of another half-bridge HB1 of the B6 module, must also be operated in a pulsed manner in order to regulate the current to the setpoint. The inductor current is freewheeled via the body diode of the high-side switch arranged above it, for example, semiconductor switch S1, of this half-bridge HB1. When the semiconductor switch S2 is closed, a current I1 flows from the AC charging station 7 via the relay contact N, the diode D2, the stator winding L2, the star point of the electric machine 2 (shown in 1 ), the stator winding L1, the semiconductor switch S2, the diode D3 and the relay contact L back to the AC charging station 7. When the semiconductor switch S2 is open, a current I2 flows from the AC charging station 7 via the relay contact N, the diode D2, the stator winding L2, the star point of the electric machine 2, the stator winding L1, the body diode of the semiconductor switch S1, the high-voltage battery 3, the diode D3 and the relay contact L back to the AC charging station 7.

10 is a schematic diagram with signals from a simulation of inverter 1 (shown in 1 ) with the circuitry, whereby the AC charging function is connected to an AC charging station 7 (shown in 1 ). The instantaneous value of the alternating voltage U_Q fed in by the AC charging station 7 is determined via a voltage measurement. Depending on the sign, the appropriate semiconductor switch S2, S4 is then controlled so that the correct current is set for each half-wave. The target current, for example, is 16 A, which should be set at the peak value of the voltage half-wave.

The diagram shows the source voltage U_Q of the AC charging station 7, the control signals Gate_S2, Gate_S4 of the semiconductor switches S2, S4 (shown in 1 ), the current I_L1 in the stator winding L1 (shown in 1 ), the current I_L2 in the stator winding L2 (shown in 1 ), the current I_Q flowing from the AC charging station 7 and the charging current I_L of the high-voltage battery 3 (shown in 1 ). The task of the PFC function of inverter 1 is to set a current for both half-waves that is proportional to the voltage curve and whose peak value is 16 A. The target current is set by comparison with a proportionally reduced value of the voltage measurement. A tolerance of, for example, +/- 1 A is specified as the maximum deviation from the target current. This means that as soon as the current in the positive half-wave is 1 A below the target value, the corresponding semiconductor switch S4 is switched on in order to increase the current I_L1, I_L2 through the stator windings L1, L2. If the current value is 1 A above the target value, the semiconductor switch S4 is opened again. In this case, the current I_L1, I_L2 freewheels through the stator windings L1, L2 via the high-voltage battery 3, so that the battery is charged.

In the negative half-wave, switching occurs with the opposite sign, i.e., as soon as the current is 1 A below the (negative) target current, semiconductor switch S2 opens. As soon as the current is 1 A above the target current, semiconductor switch S2 closes again.

11 is a schematic diagram with signals of the simulation of inverter 1 (shown in 1 ) with the circuitry during AC charging at the beginning of the positive half-wave.

12 is a schematic diagram with signals of the simulation of inverter 1 (shown in 1 ) with the circuitry during AC charging at the beginning of the negative half-wave.

If the simulation determines the voltage between the negative high-voltage potential HV- (shown in 1 ) and the potential equalization PA, it is noticeable that the negative high-voltage potential HV- during the negative half-wave is identical to the phase of the source voltage U_Q. In other words: In the negative half-wave, the HV potentials HV+, HV- (shown in 1 ) of the vehicle relative to the equipotential bonding PA = N = PE (protective conductor) according to a sine half-wave. This is also a typical behavior of a PFC. With large Y-capacitances between HV+ or HV- and PA, this would lead to a leakage current that would trigger a residual current device in a building installation. lation could trigger (equalizing current flows to the protective conductor PE).

1. 1. kleine Y-Kapazitäten im Bereich der PFC angeordnet und anschließend eine galvanische Trennung über einen isolierenden DC/DC-Wandler vorgenommen werden, oder
2. 2. ein kompensierender Strom auf dem Schutzleiter PE eingespeist werden.

To remedy this,

1. 1. small Y-capacitors are arranged in the PFC area and then galvanically isolated via an isolating DC/DC converter, or
2. 2. a compensating current is fed into the protective conductor PE.

Note to 1.: For 800V vehicles, the Y-capacitances of the vehicle must be kept lower than for 400V vehicles due to the C1 characteristic curve.

Broken down to the Y-capacitance of inverter 1 (shown in 1 ) including the electrical machine 2 (shown in 1 ) This means: For a 400V inverter, a Y-capacitance of approximately 500 nF per high-voltage potential HV+, HV- should be provided. For an 800V inverter, a Y-capacitance of approximately 50 nF to 80 nF per high-voltage potential HV+, HV- should be provided.

It is clear that the leakage current is much lower in 800V vehicles.

List of reference symbols

1

Inverter

2

electric machine

3

High-voltage battery

4

DC junction box

5

AC junction box

6

DC charging station

7

AC charging station

A

ammeter

C

DC link capacitor

D1 to D4

diode

EVSE_N

Relay contact

EVSE_P

Relay contact

Gate_S2, Gate_S4

control signal

HB1 to HB3

Half bridge

HV+, HV_P

High voltage potential, positive high voltage potential

HV-, HV_N

High voltage potential, negative high voltage potential

I1, I2, I_HV+, I_HV-, I_Q, I_L1, I_L2

Electricity

I_L

Charging current

L

Relay contact

L1 to L3

Stator winding

N

Relay contact

S1 to S6

semiconductor switches

Ri_Batt

Internal resistance

U_Q

Source voltage

Claims (10)

An electric drive system for a vehicle, comprising an electric machine (2) with three stator windings (L1, L2, L3) for driving the vehicle, a high-voltage battery (3), and an inverter (1) for converting a direct voltage of the high-voltage battery (3) into an alternating voltage for supplying the electric machine (2), wherein the inverter (1) has a B6 bridge comprising three half-bridges (HB1, HB2, HB3), each formed from two semiconductor switches (S1 to S6), to the center taps of which one of the stator windings (L1, L2, L3) is connected, wherein a DC connection box (4) for charging the high-voltage battery (3) by means of a direct voltage and/or an AC connection box (5) for at least single-phase charging of the high-voltage battery (3) by means of an alternating voltage is arranged, characterized in that - a diode (D1) or a semiconductor with a diode function is arranged between the center tap of one of the half-bridges (HB1 to HB3) and a contact of the AC connection box (5) and/or the DC connection box (4) is arranged with reverse polarity, - a diode (D2) or a semiconductor with diode function is arranged between the center tap of another of the half-bridges (HB1 to HB3) and another contact of the AC connection box (5) and/or the DC connection box (4) is arranged with reverse polarity, - one diode (D3, D4) or one semiconductor with diode function is arranged from a negative high-voltage potential (HV-) of the inverter (1) to each of the two contacts of the AC connection box (5) and/or the DC connection box (4) is arranged with forward polarity. Electric drive system according to Claim 1 , characterized in that the semiconductor switches (S1 to S6) and/or the semiconductors with diode function are designed as MOSFET or IGBT with freewheeling diode. Electric drive system according to Claim 1 or 2 , characterized in that the inverter (1) has an intermediate circuit capacitor (C). Electric drive system according to Claim 1 or 2 , characterized in that the inverter (1) has current measuring devices (A) for measuring alternating current between the center taps of the half-bridges (HB1 to HB3) and the stator windings (L1, L2, L3). Electric drive system according to one of the preceding claims, characterized in that for the voltage isolation of two conductors, including a phase conductor and a neutral conductor, of the AC connection box (5) two relay contacts (L, N) are arranged between the respective conductor and the diodes (D1 to D4) connected thereto and/or that for the voltage isolation of two conductors, including a positive potential conductor and a negative potential conductor, of the DC connection box (4) two relay contacts (EVSE_P, EVSE_N) are arranged between the respective conductor and the diodes (D1 to D4) connected thereto. Electric drive system according to Claim 5 , characterized in that in the direction of the inverter (1) one relay contact (L, N) assigned to the DC connection box (4) and one relay contact (EVSE_P, EVSE_N) assigned to the AC connection box (5) are connected to one another to form a pair. Method for charging the high-voltage battery (3) of the electric drive system according to one of the preceding claims at a DC charging station (6) with boost function, wherein the DC charging station (6) is connected to the DC connection box (4), characterized in that a semiconductor switch (S2, S4, S6) arranged as a low-side switch of one of the half-bridges (HB1, HB2, HB3), which is connected to the DC connection box (4) via one of the diodes (D1, D2), is controlled in a clocked manner. Method for charging the high-voltage battery (3) of the electric drive system according to one of the Claims 1 until 6 at an AC charging station (7), wherein the AC charging station (7) is connected to the AC connection box (5), characterized in that during a positive half-wave of an AC voltage fed in by the AC charging station (7), a semiconductor switch (S2, S4, S6) arranged as a low-side switch of one of the half-bridges (HB1, HB2, HB3), which is connected to the DC connection box (4) via one of the diodes (D1, D2), is controlled in a clocking manner, wherein during a negative half-wave of the AC voltage fed in by the AC charging station (7), a semiconductor switch (S2, S4, S6) arranged as a low-side switch of another of the half-bridges (HB1, HB2, HB3), which is connected to the DC connection box (4) via one of the diodes (D1, D2), is controlled in a clocking manner. Procedure according to Claim 7 or 8 , characterized in that when the low-side switch is open, the semiconductor switch (S1, S3, S5) arranged as a high-side switch of the same half-bridge (HB1, HB2, HB3) is closed as soon as a current flows via its body diode or freewheeling diode. Method according to one of the Claims 7 until 9 , characterized in that a target current is regulated by the timing of the semiconductor switches (S1 to S6).

Images